GB1565391A - Separation of uranium isotopes - Google Patents

Description

PATENT SPECIFICATION ( 11) 1 565 391

_I ( 21) Application No 22944/76 ( 22) Filed 3 June 1976 C ( 31) Convention Application No 50/108348 ( 19) ( 32) Filed 6 Sept 1975 in 4 M ( 33) Japan (JP) ( 44) Complete Specification published 23 April 1980 ( 51) INT CL 3 BOID 59/30 ^ ( 52) Index at acceptance CIA D 10 G 36 G 36 D 10 VD ( 54) SEPARATION OF URANIUM ISOTOPES ( 71) We, ASAHI KASEI KOGYO KABUSHIKI KAISHA, a corporation organised under the laws of Japan of 25-1, Dojimahamadori 1-chome, Kitaku, Osaka, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly

described in and by the following statement:-

This invention relates to improvements in chemical separation of uranium isotopes by use of an anion exchanger More particularly, this invention relates to a process for separating uranium isotopes by chromatography through an anion exchanger which is improved in efficiency as well as in productivity.

A chromatographic separation of uranium isotopes by use of an anion 10 exchanger and a redox system is disclosed by German Patent OLS No 2349595.

This process has not yet realized its full potential because the degree of enrichment of uranium-235 is not sufficiently high and the yielded product is too small in amount for industrial application.

Our co-pending application No 33587/76 (Serial No 1565392) describes and 15 claims a process for separating uranium isotopes in multiple stages, each stage comprising (i) an isotope exchange reaction step wherein uranium (VI) and uranium (IV) compounds are contacted in a system containing a mixed solution of said compounds, and (ii) the step of separating uranium (VI) compound enriched with uranium-235 from uranium (IV) compound after said isotope exchange 20 reaction, the uranium (VI) and uranium (IV) compounds to be contacted in each stage after the first stage being formed by reducing a portion of respective uranium (VI) compound enriched with uranium-235 isotope separated in the preceding stage and said isotope exchange reaction being accelerated by adding at least one catalyst dissolved in said mixed solution under acidic conditions wherein the 25 absolute value of the redox potential differential AE (as therein defined) is not more than one volt said catalyst being at least one selected from vanadium (III), chromium (III), manganese, (II) iron (II), copper (I), indium (III), thallium (I), tin (IV), arsenic (III), antimony (III), niobium (V), molybdenum (V), palladium (II), quinones, hydroquinones, catechols, alloxams or alloxantins, and the 30 concentration of said catalyst expressed in moles per liter being in the range from 0.5 times the absolute value of the redox potential differential AE of said catalyst to 3.0.

The object of the present invention is to provide a process for separating uranium isotopes by use of an anion exchanger which is improved in the degree of 35 enrichment per unit moving distance of the uranium adsorption zone and the amount of the product as well as in stationary operational procedures.

According to the present invention, there is provided a process for separating uranium isotopes in aqueous solution by forming a uranium adsorption zone having uranium complex anions adsorbed on an anion exchange material in contact with 40 the front boundary between an oxidizing agent zone and said uranium adsorption zone or the rear boundary between a reducing agent zone and said uranium adsorption zone, or both boundaries, the said boundaries being moved by a continuous feed of a solution of uranium complex anions or a reducing agent solution as an eluant solution thereby concentrating uranium-238 in the vicinity of 45 the front boundary, uranium-235 in the vicinity of the rear boundary or both thereof, wherein the improvement comprises accelerating the electron exchange reactions occurring in the uranium adsorption zone to the rate constant k of not less than 1 mol/liter min by use of one or more electron exchange catalysts, which are contained in the eluant solution and which are inert to reduction and oxidation 50 by uranium complex anions in said uranium adsorption zone, under the conditions whereby the selectivity coefficient Ku IVV)J is 2 or more.

In one aspect, the present invention is based on the finding that electron exchange reactions which control the degree of separation per unit moving distance of the uranium adsorption zone can be accelerated in the presence of 5 a catalyst The electron exchange reaction referred to in the specification and claims is defined by the following reaction scheme:

235 u(iv)+ 238 u(vl)K 235 u(vi)+ 238 u(lv) wherein K is an equilibrium constant:

K l 238,(,jl 235,(vj 10 l 235 U(V)l l 238 (vjl Because the equilibrium constant K is slightly larger than unity, the uranium isotopes with the mass number of 235 are concentrated in the uranyl ions in slight preference over the uranium isotopes with the mass number of 238 and vice versa in the uranous ions when the uranous ions are brought into contact with the uranyl ions The reactions occur in multiple stages of equilibrium in the system of ion 15 exchange, namely while accomplishing new equilibria from segment to segment.

For example, at the boundary between the uranium adsorption zone containing uranyl ions and the reducing agent's adsorption zone, the uranyl ion adsorbed on anion exchanger is reduced to uranous ion upon contact with the reducing agent.

The uranous ion thus formed is eluted from the anion exchange material and 20 transferred by the flow of external solution to the next segment where there occurs contact between the eluted uranous ions and the uranyl ion adsorbed on the anion exchange material, whereby one step isotope equilibrium as shown in the above scheme is attained, and uranyl ion adsorbed is enriched to a slight extent in uranium-235 When the boundary is further moved by continuing the feed of the 25 reducing agent, the uranyl ion thus enriched in uranium-235 is reduced to uranous ion, which is eluted and transferred to a further subsequent segment where the eluted uranous ion enriched in uranium-235 contacts with the adsorbed uranyl ion in said segment to accomplish another equilibrium to form uranyl ion further enriched with uranium-235 as compared with that in the previous segment By 30 repetition of such procedures, uranium-235 is gradually enriched in the vicinity of the boundary Further, at the segment which is subsequent to the nearest segment to the boundary, there occurs the enrichment of uranium-235 before contact with the reducing agent Thus, the uranous ion, which has accomplished equilibrium according to the mechanism as described above, contains uranium-235 in an 35 amount slightly larger than the uranous ion in the next segment Therefore, when said uranous ion enters into the next segment, a new equilibrium is attained to form uranyl ion which is enriched in uranium-235 In this manner, there is formed an isotope distribution wherein uranium-235 is more concentrated nearer to the boundary and less concentrated in 40 the center of the uranium adsorption zone Likewise, uranium-238 is concentrated in uranous ion in the vicinity of the boundary between the uranium adsorption zone and the oxidizing agent zone.

The first requirement to make the process for separation of uranium isotopes industrially useful is that the degree of enrichment of one isotope per unit moving 45 distance of the uranium adsorption zone should be sufficiently high In other words, for improvement in efficiency of separation, it is necessary to effect enrichment of one of the isotopes in a short moving distance of the boundary For this purpose, it has now been found desirable to accomplish most promptly the electron exchange equilibrium between the said isotopes Thus, if it takes too long 50 a time before the isotope equilibrium is accomplished between the uranyl ion adsorbed and the uranous ion in the external solution flowing in the direction of the eluant solution, the isotope once enriched is rather diffused in the system than transferred to the next segment on the anion exchanger for further enrichment, thus resulting in a decrease in the number of effective theoretical plates of 55 separation According to the methods known in the art, the speed for accomplishing the electron exchange equilibrium (hereinafter referred to as the rate of electron exchange reaction) has been extremely low, so that no sufficient I 1,565,391 theoretical number of plates can be obtained and the degree of enrichment has remained on a low level For avoidance of these drawbacks, we have found that, with the co-presence of a catalyst which elevates the rate of electron exchange reaction under appropriate operational conditions, the rate of electron exchange reaction is remarkably enhanced and the numbers of theoretical plates of 5 separation as well as the degree of enrichment are greatly increased The rate of electron exchange reaction is at least 1 mol/liter min, and preferably 3 mol/ liter min or more in terms of the rate constant k which is measured under predetermined operational conditions by the method as hereinafter described.

Electron exchange catalysts used in the present invention are: 10 (I) metal ions of iron, copper, indium, zirconium, germanium, vanadium, arsenic, molybdenum, rhenium, ruthenium, lanthanides, or the metals ions of an atomic group of the periodic table containing said metals, provided that the ions of the atomic group with zero valency are excluded; ( 2) aliphatic, aromatic, or cyclic amines such as piperidine, piperazine, 15 ethylene diamine, propylene diamine, trimethylene diamine, 1,3diaminopropane, ethanolamine, diethanolamine, aniline, p-amino phenol o, m, or p-amino phenol, o, m, or p-toluidine, p-chloro aniline, p-phenylene diamine, N-methyl pyrrole, imidazole, 2-methyl imidazole, N-methyl imidazole, pyrazole, pyridine, a,, /3, or Fpicoline, 4-ethyl pyridine, picolinic acid, nicotinic acid, oxine, oxine sulfonic acid, 20 pyrazine, triazine, etc; derivatives thereof; and salts thereof; ( 3) amino polycarboxylic acids such as imino diacetate, imino dipropionate, N-methyl imino diacetate, etc; derivatives thereof and salts thereof; ( 4) aliphatic or aromatic carboxylic acids such as formic acid, acetic acid, propionic acid, monochloro-acetic acid, oxalic acid, malonic acid, glutaric acid, 25 glycolic acid, gluconic acid, lactic acid, tartaric acid, citric acid, thioglycolic acid, salicylic acid, 5-sulfosalicylic acid, etc: derivatives thereof; and salts thereof; ( 5) aromatic oxysulfonic acids and salts thereof such as 4,5-dihydroxy-mbenzene-disulfonic acid disodium salt and chromotropic acid, ( 6) amino acids such as glycine, alanine, valine, glutamic acid, tyrosine, p 30 amino benzoic acid; and salts thereof; ( 7) amino sulfonic acids such as sulfanilic acid, sulfamic acid; and salts thereof; ( 8) /3-diketones such as acetyl acetone, and trifluoroacetyl acetone; ( 9) water-soluble, organic solvents such as formamide, N-methyl formamide, ethylene glycol, ethylene glycol monomethyl ether, methanol, ethanol, propanol, 35 acetonitrile, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran, and acetone, ( 10) quinones such as p-benzo quinone, methyl-p-benzo quinone, duroquinone, chloranyl, chloranylic acid, o-benzoquinone and, 3-napthoquinone; ( 11) polyhydroxy aromatics such as hydroquinone, methyl hydroquinone, 40 catechol and resorcinol ( 12) alloxans, such as alloxan, methyl alloxan, ethyl alloxan; alloxantin, and methyl alloxantin.

These electron exchange catalysts can be used either alone or in combinations of two or more catalysts Among these, the following groups of catalysts are 45 particularly preferred as effective catalysts to be used in the process of the invention.

(a) metal ions of iron, molybdenum, vanadium, copper, indium, rhenium, yttrium, ruthenium, arsenic; or the metal ions of atomic groups of the periodic table containing said metals, provided that the atomic groups with zero valency are 50 excluded; (b) aliphatic, aromatic, cyclic amines such as piperidine, piperazine, ethylenediamine, propylenediamine, 1,3-diaminopropane, ethanolamine, pphenylenediamine, imidazole, pyridine, a, P, or y-picoline, derivatives thereof; and salts thereof; 55 (c) aliphatic or aromatic carboxylic acids such as acetic acid, gluconic acid, tartaric acid, citric acid, 5-sulfosalicylic acid; derivatives thereof; and salts thereof; (d) aromatic oxysulfonic acids and salts thereof such as 4,5-dihydroxy-mbenzene-disulfonic acid disodium salt and chromotropic acid; 60 (e) water-soluble organic compounds such as ethylene glycol, methanol, ethanol, propanol, acetone and acetonitrile:

(f) quinones such as p-benzo quinone, duro-quinone, chloranyl, chloranylic acid and 3-naphthoquinone:

1,565,391 1,565,391 (g) polyhydroxy aromatics such as hydroquinone, catechol and resorcinol; (h) alloxans, such as alloxan, methyl alloxan, alloxantin and methyl alloxantin.

Examples of preferred combinations are as follows:

I One or more in Group (a)-One or more in Groups (b) to (d) II One or more in Group (a)-One or more in Group (e) III One or more in Group (a)-One or more in Groups (f) to (h) IV One or more in Groups (b) to (d)-One or more in Groups (f) to (h) V One or more in Groups (b) to (d)-One or more in Group (e) VI One or more in Groups (f) to (h)-One or more in Group (e) Above all, when ions of iron are used alone or in combination with other metal ions and/or other catalyst compounds, a remarkable acceleration effect can be attained.

Table I shows some examples of k values which are measured by the method as hereinafter described for various electron exchange catalysts.

Catalyst No.

TABLE 1

Electron exchange catalyst concentration compounds (M) 1 pyridine 2 pyperidine 3 imidazole 4 p-phenylenediamine a-picoline 6 chloranylic acid 7 hydroquinone 8 citric acid 9 3-naphthoquinone cuprous chloride 11 molybdenum dichloride 12 ferrous chloride 13 ferrous chloride p-naphthoquinone 14 pyridine citric acid ferrous chloride acetone 0.5 0.8 0.4 0.5 1.0 0.01 0.5 1.0 0.01 0.2 0.01 0.15 0.15 { O 01 0.5 1.0 { 1 0 pt.2 V/V% Proton concen tempera k tration ture (l/mol.

(M) ( C) min) 4.0 90 0 11 4.0 90 3 4.0 90 2 4 4.0 90 2 2 4.0 90 2 7 4.0 90 3 8 4.0 80 5 2 4.0 90 2 6 4.0 90 1 1 4.0 70 4 6 4.0 70 1 7 4.0 90 5 5 4.0 70 1 3 4.0 70 7 4 4.0 90 4 8 2.0 70 29 The catalytic effect of each of the catalysts as enumerated above is generally in direct proportion to the concentration thereof which is to be determined by taking various factors such as the desired electron exchange rate constant, the solubility of the catalyst employed, the selectivity coefficient as described below, etc into account A metal ion chosen from the class ( 1) can be used in the form of any ion irrespective of its valency However, in cases where the oxidationreduction potential of the metal used is higher than that of uranium, the uranous ion can be oxidized to uranyl ion by oxidative ions to change the ratio of the concentration of uranous ion to that of uranyl ion in the solution Accordingly, in such a case, it is desirable to add the metal in the form of reductive ions For example, vanadium is allowed to be present as a trivalent ion in an aqueous hydrochloric acid solution with the concentration of 2 mol/liter On the contrary, when the oxidationreduction potential of the metal used is higher than that of uranium, the uranyl ion can be reduced to uranous ion by reductive ions to change said ratio Accordingly, in such a case, the catalyst is added in an oxidized form For example, it is added as a tetravalent ion, and not as a divalent ion Thus, the catalyst is required to be inert to reduction and oxidation of uranium ions in the solution Furthermore, a metal ion of the kind which forms coordination bonds with chemical species present in the system having co-ordinating ability should be added in a relatively low concentration This is because highly negative anion complexes thus formed are adsorbed on the anion exchanger to affect badly the efficiency of separation In a system wherein hydrochloric acid and water are used, such ions as V(V), Zr(IV), Mo(VI), Re(VII), Sb(III), Sb(V), Cu(I), Ge(IV), Bi(III), Ru(IV) can form complexes with Cl ion to be adsorbed on the anion exchanger Therefore, when the catalyst is chosen from these metal ions, its concentration should be controlled to at most O 5 mol/liter in the solution With other metal ions, it is generally possible to vary widely the concentration, preferably in the range from 0 01 to 3 mol/liter Typical metal ions which exhibit a remarkable acceleration effect by the addition of lesser amounts 5 are those of iron, molybdenum, vanadium, copper, rhenium, yttrium, ruthenium and arsenic Some of the organic compounds are set forth in classes ( 2) to ( 4) and ( 6) to ( 8) have larger dissociation constants as well as larger complex stability constants These compounds can readily form complexes with the uranyl or uranous ion and therefore they should be used under highly acidic conditions, for 10 example, in an aqueous hydrochloric acid solution with a concentration of 1 to 6 mol/litre In general, the amount of the catalyst chosen from said organic compounds can be varied within the range from 0 001 to 3 mol/liter, preferably from 0 01 to 2 mol/liter The catalyst chosen from the organic solvents of the class ( 9) can be used in amounts ranging from 1 to 95 VN%, preferably from 5 to 80 15 The rate of electron exchange reaction is affected also by the proton concentration in the system For example, in a system wherein hydrochloric acid is used, k is at its minimum when the proton concentration is in the range from 2 to 4 mol/liter and increases when the proton concentration is lower or higher than said 20 range However, in case of a lower proton concentration, hydrolysis of uranium ion, oxidizing agent or reducing agent is liable to occur, while in case of a higher proton concentration than 6 mol/liter, on the other hand, it is difficult to obtain a sufficiently high selectivity coefficient as described below The proton concentration can be adjusted by use of at least one acid such as hydrochloric acid, 25 hydrobromic acid, sulfuric acid, hydrofluoric acid, etc In view of the higher selectivity coefficient to be attained, hydrochloric acid or hydrobromic acid is preferably used in amounts ranging from 1 to 6 mol/liter.

The rate of electron exchange reaction is increased as the temperature is raised Since the activation energy of said reaction is considerably large in the 30 order of 10 to 40 Kcal/mol, it is preferred to conduct the reaction at a high temperature However, various troubles such as the formation of precipitates through hydrolysis of uranium, oxidizing agent or reducing agent, deterioration of the ion exchanger, decrease in selectivity coefficient, etc are liable to be caused at higher temperatures Thus, although it is possible to conduct the reaction at 100 to 35 'C, it is preferred to operate separation procedures at 600 to 1500 C.

The concentrations of various components as specified in the specification and claims are in moles per liter of the external solution in contact with anion exchanger, unless otherwise indicated.

According to the present invention, it is also required to operate separation 40 procedures under conditions which afford adsorption power of uranyl ion to an anion exchanger in the system sufficiently higher than that of uranous ion In other words, the selectivity coefficient M 1 Vv} as defined by the following formula is required to be at least 2, preferably 5 or more.

Ku(vl I 45 U(VI)s U(IV), wherein U(VI)R and U(IV)R are uranyl ion concentration and uranous ion concentration in an anion exchanger, respectively; and U(VI), and U(IV), are uranyl ion concentration and uranous ion concentration in external solution in contact with said anion exchanger, respectively By the term "external solution" is meant the solution present in the space other than that occupied by ion exchange 50 material namely in interstices between the resin particles.

Generally speaking, the above selectivity coefficient Mv I' is desirably as large as possible for suitable distribution of both uranyl and uranous ions in the ion exchanger phase and the external solution phase in contact with said ion exchanger phase For example, we now consider a case where uranyl ion adsorbed 55 on an anion exchanger contacts with a reducing agent to be reduced to uranous ion while being eluted and flown in the direction of the eluant flow If said coefficient is not large enough in this case, uranyl ion cannot efficiently be retained on the anion exchanger but uranous ion can occupy a considerable part of the adsorption sites thereof As a result, in the vicinity of the boundary 60 I 1,565,391 in contact with a reducing agent, reduction of uranyl ion is rendered difficult to decrease the chances of contact of uranyl ion with uranous ion Thus, only under conditions permitting a sufficiently higher selectivity coefficient, an efficient electron exchange reaction can be made possible.

There are various factors which can affect the selectivity coefficient KU'tv' 5 For example, as already mentioned, the proton concentration in the system or the temperature employed has a remarkable effect on the selectivity coefficient.

Depending on the electron exchange reaction catalyst to be used as well as its concentration, the selectivity coefficient can also greatly be varied Although it is not yet theoretically established, there seems to be a correlation between the types 10 of the catalyst and the selectivity coefficient.

According to the present invention, it has been found that the principle of the invention can be applicable to three modes of the process, namely:

(A) a process wherein an adsorption zone of a reducing agent is provided at the rear end of, and adjacent to, an adsorption zone of uranium complex anions in a 15 system of an anion exchanger to conduct reduction of hexavalent uranium anions to tetravalent uranium anions at the boundary therebetween to concentrate uranium-235 in the vicinity of said boundary while displacing said boundary through said anion exchanger; (B) a process wherein an adsorption zone of an oxidizing agent is provided at 20 the front end of and adjacent to, an adsorption zone of uranium complex anions in a system of an anion exchanger to conduct oxidation of tetravalent uranium anions to hexavalent uranium anions at the boundary therebeween to concentrate uranium-238 in the vicinity of said boundary while displacing said boundary through said anion exchanger; and 25 (C) a process wherein an adsorption zone of uranium complex anions is formed between adsorption zones of a reducing agent and an oxidizing agent at the rear and front ends, respectively, of the uranium adsorption zone and uranium-235 and uranium-238 are concentrated in the same manner as in the modes (A) and (B), respectively 30 The process of the mode (A) can be practised by, for example, charging first an aqueous solution containing uranyl complex anion into a system of an anion exchanger to form an uranium adsorption zone and then passing as eluant an aqueous reducing agent through said uranium adsorption zone, whereby there is formed a boundary (reduction boundary) between the uranium adsorption zone 35 and the reducing agent zone which moves in the direction of the eluant flow The process of the mode (B) can be practised by, for example, charging an aqueous oxidizing agent solution into a system of an anion exchanger to form an adsorption zone of oxidizing agent and then passing an aqueous solution containing uranous complex anion as eluant through the adsorption zone of the oxidizing agent, 40 whereby there is formed a boundary (oxidation boundary) between the adsorption zone of the oxidizing agent and the uranium adsorption zone which moves in the direction of the eluant The process of the mode (C) can be practised by, for example, charging first an aqueous oxidizing solution into a system of an anion exchanger to form an adsorption zone of oxidizing agent and then passing an 45 aqueous solution containing uranous complex anion as eluant through the adsorption zone of the oxidizing agent, followed further by charging an aqueous reducing agent solution, whereby there are formed both oxidation and reduction boundaries in the forward and rearward parts of the uranium adsorption zone, respectively, in the direction of the eluant flow, which move simultaneously 50 in the same direction as the eluant flow.

The oxidizing agent suitable for the present process is chosen from those which can promptly oxidize uranous ion to uranyl ion in an anion exchanger as well as in the external solution Typical examples of such oxidizing agents are divalent copper salts, trivalent iron salts, tetravalent cerium salts, divalent manganese salts, 55 tetravalent vanadium salts, hexavalent molybdenum salts and trivalent thallium salts The concentration of the oxidizing agent in the external solution can be varied from 0 02 to 2 0 mol/liter corresponding to the concentration of uranium ion in the external solution which is variable from 0 01 to 1 0 mol/liter.

On the other hand, the reducing agent suitable for the present process is 60 chosen from those which can promptly reduce uranyl ion to uranous ion in an anion exchanger as well as in the external solution Typical examples are trivalent vanadium salts, pentavalent molybdenum salts, trivalent titanium salts, and divalent tin salts The concentration of the reducing agent can be varied from 0 02 m f I 1,565,391 to 1 0 mol/liter corresponding to the concentration of uranium ion in the external solution which is variable from 0 01 to 1 0 mol/liter.

Examples of anion exchanger usable in the process of the present invention are strongly basic anion exchange resins having quaternary ammonium groups prepared by chloromethylating styrene-divinyl benzene copolymers, followed by 5 amination; and weakly basic anion exchange resins having primary or tertiary amine groups.

The anion exchangers to be used in the present invention are desired to have preferred adsorption power for uranyl ion over uranous ion and also to be small in degree of swelling or shrinking when contacted with various solutions such as of 10 oxidizing agent, reducing agent or uranium ions Furthermore, they should effect rapid adsorption and desorption enough to prevent once separated isotopes from re-mixing.

The uranium ion concentration in the external solution can be varied from 0 01 to 1 0 mol/liter, preferably from 0 10 to 0 50 molliter, more preferably from 15 0.10 to 0 40 mo V liter The concentration of uranium ion is determined by considering desired product yield and the flow rate constant which is determined by dividing the linear velocity of the eluent by the moving speed of the uranium adsorption zone It has been found that the degree of enrichment per unit moving distance is improved by decreasing the flow rate On the other hand, by decrease of 20 the flow rate, the amount of the product obtained in unit time is decreased.

Therefore, it is necessary to increase the concentration of uranium ion as well as those of oxidizing agent and reducing agent, correspondingly, in order to maintain the flow rate constant, namely to maintain the product yield at a constant level when the flow rate constant is decreased However, if the uranium ion 25 concentration is too high, namely exceeding 1 0 mol/liter, unfavourable phenomena are found to occur in the vicinity of the boundaries That-is, near the reduction boundary, uranous ions formed by reduction of uranyl ions cannot completely be eluted and left behind the boundary, or alternatively, near the oxidation boundary, uranyl ions formed by oxidation of uranous ions cannot 30 sufficiently be retained on the ion exchanger but penetrate into the adsorption zone of the oxidizing agent Thus, in either case, separation efficiency is decreased due to insufficient contact between uranyl and uranous ions in the vicinity of each boundary.

Furthermore, the ratio of uranous ion concentration to uranyl ion 35 concentration (hereinafter referred to as -reduction ratio R") in the externalsolution as hereinbefore defined is found to affect the separation efficiency The reduction ratio R" refers to the ratio of uranous ion concentration to uranyl ion concentration in the external solution as hereinbefore defined, in the uranium adsorption zone in a steady state This steady state is accomplished after a 40 boundary or boundaries are formed between the uranium adsorption zone and oxidizing agent and/or reducing agent The ratio is substantially constant under the predetermined condition while it is moved by an eluant in the direction of the flow of the eluant and thus in the direction of the adsorption zone out of the column.

Practically, measurements of several fractions of the effluents from the entire 45 uranium adsorption zone are conducted and the average ratio from those results is determined as the ratio in a steady state The reduction ratio R" is closely correlated with the selectivity coefficient Kusv J The separation efficiency is found to be at its maximum when the reduction ratio k is substantially equal to the square root of the selectivity coefficient The reduction ratio R can be optimized easily 50 by adjusting the concentration of the reducing agent or the ratio of uranous ion concentration to uranyl ion concentration of the feeding uranium solution to a suitable value.

When the operation is performed at a temperature of 600 C or higher, some of the metal ions used as reducing agent or oxidizing agent are liable to be hydrolysed 55 to form precipitates These precipitates are not favorable since they are accumulated in the system and greatly increase the pressure drop, that is the difference in pressure between the inlet and the outlet of the column, and also cause other unfavourable phenomena Especially, when there is used as reducing agent trivalent titanium which is preferable because of its excellent characteristics 60 (excellent selectivity, large rate of reduction, etc), precipitates are gradually formed by being heated in a strongly acidic solution Some of the organic compounds are found to be effectively added for prevention of precipitate formation They include aliphatic polycarboxylic acids such as oxalic acid, tartaric acid, citric acid, malonic acid, glutaric acid, succinic acid, maleic acid, fumaric 65 I 1,565,391 acid, and salts thereof; aromatic carboxylic acids such as salicylic acid, 5sulfosalicylic acid, and salts thereof; polyhydroxy aromatic compounds such as catechol, resorcinol, 4,5-dihydroxy-benzene-disulfonic acid disodium salt, and chromotropic acid; monosaccharides, alkyl derivatives thereof, derivatives obtained by oxidation or reduction thereof, or salts of these derivatives, 5 e.g glycose, fructose, mannose, galactose, arabinose, ribose, xylose, erythrose, sorbitol, mannitol, arabitol, glucono-S-lactone, glucono-ylactone, gluconic acid, mannonic acid, uronic acid, a-keto gluconic acid, and methyl glucoside Such a compound is added in an amount ranging from 0 1 to 3 mol/liter.

Some of the organic compounds as mentioned above have also an effect of 10 accelerating the electron exchange reaction Therefore, when such a compound is used as the catalyst for the electron exchange reaction, there is no need further to add a precipitation preventing agent.

In practising the process of the present invention, conventional ionexchange columns can be used A preferred ion-exchange column for practice of the 15 invention is a corrosion-resistant vessel coated with heat insulating material on the surface and equipped with a jacket for passing heat transfer medium to keep the column at a constant temperature The shape and the size of the vessel are not particularly limited, but the shape should be determined in due consideration of the uniform flow of eluant solution as well as the ease of operation The size is 20 determined mainly from the desired product yield In order to afford uniform flow of solutions through the bed of anion exchange resins, the column is preferably equipped at the inlet with a distributor Furthermore, it is preferably equipped at the outlet with a filter and a collecting plate, in order to collect the eluant solution uniformly from all of the cross-sectional area of the column When the ion 25 exchange columns have both of these devices as mentioned above provided at the inlet and outlet, respectively, they should be provided in a manner such that there should be little dead space between said distributor and the resin bed and between the collecting plate and the resin bed Two or more columns combined can also be used, especially in continuous operations 30 Referring now to operational procedures of the process according to mode C as mentioned above, an oxidizing solution is in the first place fed to an anion exchange column packed with anion exchanger Preparation of the anion exchange column is carried out generally in the following manner Anion exchange resin particles, from which remaining impurities (e g organic solvents, metals, etc) are 35 eliminated, are purified by washing with methanol, hydrochloric acid or sodium hydroxide, etc Packing of anion exchange resins can be conducted either by wet packing with solvents or by dry packing The solvents used in wet packing are not restricted and are generally chosen from at least one of the hydrochloric acid solutions, oxidizing agent solutions, uranium complex anion solutions, reducing 40 agent solutions, water and organic solvents Into the said solvent, anion exchangers are poured to form a slurry solution The slurry solution thus formed is packed in the column by gas pressure, pump, or sedimentation On the other hand, in case of dry packing, the ion exchangers after dehydration or drying are thrown into the column and the air contained in the column is replaced completely with the solvent 45 as used in wet packing as mentioned above Packing should be conducted so as to form a uniformly packed bed, and for this purpose, such methods as high speed packing of slurry solution or packing with vibration are frequently employed On the other hand, the oxidizing solution is prepared by mixing an oxidizing agent, an inorganic acid and water (together with other substances such as organic solvents, 50 etc if desired) in predetermined concentrations, respectively The feeding speed of the oxidizing agent solution is controlled by adjusting the valve equipped at top or bottom of the column or by feeding with a constant flow rate pump The adsorption speed (the moving speed of the frontal boundary of the oxidizing agent adsorption zone) is not particularly limited But, when two or more columns are employed for 55 continuous operation and anion exchangers in these columns are converted successively to the form of oxidizing agent, the next column must be changed to the form of oxidizing agent while the uranium adsorption zone passes through the preceding column Therefore, the absorbing speed of the oxidizing agent is often determined so as to be larger than the moving speed of the uranium adsorption 60 zone The absorbing speed of the oxidizing agent solution can be varied widely when all of the columns are converted to the form of oxidizing agent at the same time.

When the frontal boundary of the oxidizing agent adsorption zone is observed to reach one end (top or bottom) of the column, or the concentration of the oxidizing 1,565,391 agent solution outflown from the end becomes nearly equal to the feed concentration, the feed of the oxidizing agent solution is discontinued.

As the second step, after the oxidizing agent adsorption zone is formed by the above operation, a uranium complex anion solution containing uranous ion is supplied to the column Uranium solution is prepared by mixing concentrated 5 uranous solution (and concentrated uranyl solution, if desired) and water (together with other substances such an electron exchange catalyst, organic solvents, etc) in predetermined concentrations, respectively The moving speed of the frontal boundary of uranium adsorption zone is adjusted to a determined value by controlling the flow rate similarly to that described above in supply of the oxidizing 10 agent solution As long as the supply of uranium solution is continued, the boundary between uranium adsorption zone and oxidizing agent adsorption zone moves through the column, usually keeping a clear boundary The feeding of uranium solution is discontinued before the boundary reaches the end of the column opposite to the direction of eluant flow 15 As the third step, a reducing agent solution is fed to the column, whereby a uranium adsorption zone is formed between the oxidizing agent zone and the reducing agent zone The reducing agent solution is prepared by mixing a reducing agent, an electron exchange catalyst and water (together with other substances such as organic solvents, precipitation preventing agent, etc) in predetermined 20 concentrations, respectively It is critically required that the reducing agent solution should contain an electron exchange catalyst in order to obtain an increased rate constant for the separation effect Uranium-235 is concentrated in the vicinity of the rear boundary and uranium-238 in the vicinity of the frontal boundary The length of the uranium adsorption zone is controlled desirably depending on the 25 moving distance The flow rate of the reducing agent solution is determined to be approximately the same as that of uranium solution, but sometimes slightly modified according to the moving speed of the boundary Feeding of the reducing agent solution is continued until the uranium solution ceases to flow out from the end of the column 30 As mentioned above, the operation is usually conducted by moving the boundary within a finite distance with two or more columns combined, but the operation can also be conducted by moving the boundary for a non-finite distance by adoption of a recycle system.

Alternatively, for operation of the process of mode (A), the procedures as 35 described above in the first and the second steps can be followed In this case, however, feeding of the uranium solution is continued until the oxidation boundary reaches the outlet of the column (that of the last column in the case of plural columns combined).

On the other hand, the process of mode B is operated by first feeding a 40 uranium solution to the anion exchange column The uranium solution fed in this case is prepared by mixing concentrated uranyl solution (and concentrated uranous solution, if desired), an electron exchange catalyst and water (together with other substances such as organic solvents, etc if desired) Then, the reducing agent solution is fed to the adsorption zone of uranium thus formed, whereby a reduction 45 boundary is formed in the rear part of the adsorption zone The procedure for moving the boundary and other operations are substantially the same as described in the third step of the process according to mode C.

The present invention is described in further detail by the following Examples and Comparative Examples, wherein measurements of various factors are 50 conducted in the following manner:

I k(rate constant of electron exchange reaction):

The electron exchange reactions involved herein should in more strict sense include not only those in the external solution, but also those between the interior and the exterior of the anion exchanger But, since the rate of electron exchange in 55 the external solution is closely correlated with that of electron exchange reaction between the interior and the exterior of ion exchanger, a catalyst having a large rate of electron exchange measured in the solution is generally confirmed to have a large rate also in the system containing the ion exchanger Accordingly, in the present invention, the rate constant k is measured in a solution in the following 60 manner.

In a thermostat chamber kept at a predetermined operational temperature are provided two flasks, one of 200 ml and the other of 50 ml Twenty ml of an aqueous uranyl solution are prepared and introduced into the 200 ml flask, which is then Q I 1,565,391 flushed with nitrogen The solution contains depleted uranyl ion with an isotope mol fraction of 0 4658 % (lU(VI)I= O 1 mol/liter) and is conditioned under operational conditions by adding a predetermined amount of a catalyst to be used and a predetermined amount of hydrochloric acid It should be noted that the uranyl solution need not necessarily have an isotope mol fraction of 0 4658 % 5 Similarly, twenty ml of an aqueous uranous solution are prepared from natural uranous ion with an isotope mol fraction of 0 7200 % (lU(IV)l= O 1 mol/liter) and conditioned in the same manner as in case of the uranyl solution This uranous solution is introduced into the 50 Ml flask, which is then flushed with nitrogen.

After about 15 minutes, the whole amount of the uranous solution is transferred 10 promptly into the 200 ml flask and mixed thoroughly with the uranyl solution One minute after the addition, the 200 ml flask is taken out quickly from the thermostatic chamber and the mixture is poured into a flask of 200 ml containing 40 ml of 4 mol/liter of hydrochloric acid which has previouisly been cooled to 00 C on an ice-bath to terminate the reaction Immediately thereafter, the resultant mixed 15 solution is passed through a glass column of 3 cm in diameter and 10 cm in length packed with a strongly basic anion exchange resin of quaternary ammonium type styrene-divinyl benzene copolymer with a crosslinking degree of 4 and having an ion exchange capacity of 4 3 milliequivalent/gram and being 100 to 200 mesh in size, to separate uranyl ion only by adsorption and the effluent of the aqueous 20 uranous solution is recovered from the column bottom The isotope mol fraction is determined as X, by measurement of this sample by mass spectrometry.

The exchange ratio F is defined and calculated by the following equation:

xt-xx F=cXX wherein X, denotes the isotope mol fraction of uranous ion at initiation, namely, 25 0.7200 %, Xt that after a lapse of t minutes, and X that at equilibrium, namely 1/2 x ( 0.7200 + 0 4658)= 0 5929 %.

The rate constant k is calculated from the isotope exchange ratio F by the following equation:

-ln(l-F) 1 K x-(liter/mol min) 30 lU(IV)l+lU(VI)l t wherein lU(IV)l and lU(VI)l are concentrations of uranous and uranyl ions, namely each being equal to 0 1 mol/liter, and t is the time of the reaction, namely one minute.

II K Wav (selectivity coefficient) One gram of a dry resin to be used is weighed into a column equipped with a 35 jacket, having an inside diameter of 10 mm and a length of 100 mm While the column is kept at a predetermined operational temperature, 300 ml of IN aqueous hydrochloric acid solution are passed therethrough, followed by washing with 500 ml of pure water.

A conc uranous solution is prepared by dissolving metallic uranium in conc 40 hydrochloric acid and removing by filtration the small quantity of precipitates produced A conc uranyl solution is prepared by oxidation of the uranous solution prepared in the aforesaid manner, namely by adding a slight excess of hydrogen peroxide and boiling the mixture for 30 minutes A mixture is prepared by blending these uranous and uranyl solutions and further adding water, electron exchange 45 catalysts and other additives to be used in the operational procedure For the purpose of measurement, the concentrations of uranous ions and uranyl ions are made equal and the total concentration is adjusted to the uranium ion concentration in the external solution as hereinbefore defined at the time of operation of chromatography The mixture thus prepared is passed through the 50 column as mentioned above sufficiently for the uranium ions to be adsorbed to the equilibrated adsorption amount Then, dry nitrogen gas is passed through the column to remove the uranium solution ions outside of the resin The adsorbed uranium ions are eluted with 1 mol/liter aqueous hydrochloric acid into a vessel provided at the bottom of the column To a portion of the eluant, a small quantity 55 of 3 % aqueous hydrogen peroxide solution, 20 % aqueous sodium hydroxide solution and 20 % aqueous sodium carbonate solution is added, thereby developing the yellow colour, and then the total concentration of uranium is measured by colorimetric analysis at 390 mn On the other hand, the concentration of uranous L 565 391 ion is determined by colorimetric analysis at 650 my of a portion of the eluant collected The concentration of uranyl ion is determined as the difference between these concentrations From the values of the concentrations of the uranium ions in the resin thus determined and those of the solution, the selectivity coefficient is S calculated 5 III R(reduction ratio) In a chromatographic column packed with an anion exchanger, an aqueous solution ( 0 1 mol/liter) of uranyl ion having a natural isotopic ratio r O is supplied sufficiently to form a uranyl ion adsorption zone After uranyl ions are equilibrated between the solution and the anion exchanger, a reducing agent solution with a 10 predetermined concentration is supplied as an eluant solution to elute uranyl ions while conducting the reduction thereof The eluted effluent from the bottom of the column is collected in fractions with the same amount of each fraction With a portion of these fractions, the total uranium concentration and the uranous concentration are analysed quantitatively by colorimetric analysis Further with a 15 portion of these fractions, the isotope mole fraction is determined by mass spectrometer From the chromatogram depicted from these results, the average reduction ratio R is calculated.

IV E(Effective separation factor) From the uranium concentration curve and the uranium isotope distribution 20 curve made from the data obtained in the measurement of R as described above, the total amount of uranium contained in the anion exchanger (Q mol) and the total amount of uranium-235 separated (D) are determined, respectively The effective separation factor is calculated by the following equation:

D 1 E=-_ _ 25 Q-D r, Example 1

To a four-necked flask of 4 1 capacity, 2000 g of water and 2 5 g of methyl cellulose were introduced, and then 3 8 g of azobisisobutyronitrile, 60 g of divinyl benzene, 10 g of ethyl vinyl benzene, 130 g of 4-vinyl pyridine and 550 g of dimethyl terepthalate were introduced, to form oily particles Then, polymerization was 30 effected at 701 C for 60 hours After polymerization, the product was cooled and was thoroughly washed in a resin washing column equipped with a filter with 101 of methanol and 100 1 of water The exchange capacity of the thus obtained resin was 3.75 milliequivalent/g.

In a chromatographic column equipped with a jacket, having a diameter of 20 35 mm and a length of 1200 mm, with a filter at the bottom, the aforesaid resin was filled up to the height of 1000 mm, and then aqueous 6 N hydrochloric acid was passed therethrough for washing.

An oxidizing agent solution containing ferric chloride lFe(III)l as oxidizing agent, a uranium solution containing uranous ion lU(IV)l and a reducing agent 40 solution containing titanium trichloride lTi(III)l (obtained by dissolving spongy.

titanium in a conc HCI) as reducing agent were prepared Each solution was made in an aqueous hydrochloric acid solution and ferrous chloride is added to each solution together with P-naphthoquinone as electron exchange catalyst The composition of each solution is as shown below: 45 oxidizing agent solution:

ferric chloride Fe(III) 0 08 M ferrous chloride Fe(II) 0 80 M /-napthoquinone 002 M hydrochloric acid 3 5 M 50 uranium solution:

uranous ion lU(IV)l 0 20 M ferrous chloride 0 80 M P-napthoquinone 0 02 M hydrochloric acid 3 5 M 55 reducing agent solution:

titanium trichloride Ti(III) 0 30 M ferrous chloride 0 80 M B-napthoquinone 0 02 M hydrochloric acid 3 5 M 60 1 1 I 1,565,391 1 1 By supplying the oxidizing agent solution to the column kept at 900 C, the whole of the anion exchanger was substituted with the oxidizing agent.

Subsequently, the uranium solution was supplied so as to oxidize uranous ion to uranyl ion by contacting with the oxidizing agent, whereby uranyl ion was adsorbed onto the anion exchanger The uranium adsorption zone was gradually enlarged, as 5 the supply of the uranium solution, and after reaching 50 cm, the supply of the uranium was stopped Then, by supplying the reducing agent solution to the column, the uranyl ion adsorbed was reduced at the rear boundary to uranous ion, which after moving in a direction of eluant procession to the front boundary, was again oxidized to uranyl ion and adsorbed 10 As long as the supply of the reducing agent solution was continued, the uranium adsorption zone continued to move until the front boundary of the uranium adsorption zone reached the bottom of the column The uranium solution outflow from the outlet of the column was collected in fractions each of 5 ml When the reducing agent solution began (after the outflow of the rear boundary of the 15 uranium adsorption zone) to outflow, the supply of the reducing agent solution was stopped During the operation, the flow rate of the eluant was maintained at 309 ml/hour, and the boundary moving speed was 10 3 m/day.

The concentration of the sample, collected, analysed quantitatively by the fluorescent X-ray analysis and the colorimetric analysis, was almost constant 20 except for the vicinity of the boundary Thus, the uranyl concentration was 0 049 M, and the uranous concentration was 0 145 M Under these conditions, k and Kulv) were measured to be 41 l/mol min and 11, respectively.

Further, the isotope ratios ( 235 U/238 U) of the fractions closest to the front and rear boundaries, measured by mass spectrometer, were 0 006806 in the vicinity of 25 the front boundary and 0 007704 in the vicinity of the rear boundary which were 0.9385 times and 1 0623 times, respectively, as large as the natural isotope ratio 0.007252.

If the separation effect is defined by the degree of enrichment per 1 meter (%/m) multiplied by the boundary moving speed (m/day), the separation effect was 30 nearly 15 to 40 times larger than that of Example 1 in German Patent OLS No.

2349595.

Control 1 Separation of uranium isotope was conducted in the same manner as in Example 1 except that no electron exchange catalyst, i e ferrous chloride and p 35 naphthoquinone, was added to each solution and the flow rate and the moving speed of the boundary were 161 ml/hr, 5 1 m/day respectively Under these conditions, k and Ku,'v O were measured to be 0 08 1/mol min and 9 8, respectively.

The isotope ratios U 35 U/238 U) were 0 007188 in the vicinity of the front boundary and 0 007309 in the vicinity of the rear boundary 40 Examples 2-8

Into a four-necked flask, 2000 g of water, 2 5 g of methyl cellulose, 1 2 g of gelatin, 12 g of sodium chloride and 15 g of sodium pyrophosphate were charged and mixed under stirring Into this mixture was stirred a polymerizing solution, comprising 4 3 g of azobisisobutyronitrile, 200 g of isoamyl acetate, 40 g of n 45 heptane, 20 g of styrene, 16 g of ethyl vinyl benzene and 144 g of 2vinyl pyridine, thereby to form a suspension of oily particles Polymerization was effected at 700 C for 60 hours, followed by thorough washing in a column equipped with a filter with 201 of benzyl alcohol, 201 of methanol and 2001 of water The exchange capacity of the resin thus prepared was 4 58 milliequivalent/g 50 Into a chromatographic column equipped with a jacket having a diameter of mm and a length of 1200 mm, the above resin was filled up to the height of 1000 mm and then was thoroughly washed with aqueous 6 N hydrochloric acid.

The uranium solution and the oxidizing agent solution having the composition as described in Table 2 were prepared The uranium solution was supplied to the 55 column kept at 90 C thereby adsorbing uranyl ion, and then the reducing agent solution was supplied, thereby moving the boundary of the uranium adsorption zone and the reducing agent adsorption zone When the boundary reached the bottom of the column, every 5 ml of the outflowing uranium solution was collected.

The isotope ratio in the vicinity of the boundary was measured, and the result was 60 shown in Table 3 below.

I 1,565,391 l 1) TABLE 2 proton the concen the concen concen electron exchange catalyst Example tration of tration of tration concen k(l/ No U(VI) (M) Ti(III) (M) (HCI) (M) compounds tration mol min) Kuov, 2 0 10 0 40 4 Fe C 12 0 75 (M) 37 11 8 pyridine 0 30 (M) 3 O 15 0 30 3 5 VCI 3 0 20 (M) 17 8 7 acetic acid 5 (V/V%) 4 0 10 0 30 3 5 Cu CI 0 05 (M) 10 6 2 a alloxan 0 1 (M) 0 08 0 30 3 0 Fe C 12 1 5 (M) 85 9 5 6 0 20 0 60 3 5 hydroquinone 0 4 (M) 4 5 10 9 citric acid O 5 (M) 7 0 10 0 40 2 5 Mo C 12 O 05 (M) 41 13 4 n-propanol 30 (V/V%) 8 0 10 0 20 4 0 imidazole O 5 (M) 5 1 7 9 ethylene diamine 0 4 (M) 9 0 10 0 35 2 5 Fe C 12 1 O (M) 62 9 1 a-picoline 0 3 (M) 1,565,391 TABLE 3

Exam the boundary pie moving speed No (m/day) 2 15 8 3 21 3 4 13 9 15 9 6 33 4 7 17 3 8 10 2 9 9 8 appearance of the boundary clear slightly unclear slightly unclear clear clear slightly unclear clear clear isotope ratio ( 235 U/238 U) 0.007580 0.007440 0.007427 0.007725 0.007352 0.007487 0.007468 0.007808 separation effect (times larger than control 1) 18 14 8 26 12 14 8 Control 2 Anion exchanger used in Examples 2-9 was filled in a column and the experiment was conducted in the same manner as in Examples 2-9, except that the uranium solution and the reducing agent solution with the following composition were used.

uranium solution:

U(VI) 0 03 M, V C 13 0 2 M, hydrochloric acid 8 M; reducing agent solution:

Ti(III) 0 06 M, VCI 3 0 2 M, hydrochloric acid 8 M Under these conditions k was 5 4 and KU,,', was 0 95 At a lapse of a certain time after the supply of oxidizing agent solution, the boundary becomes unclear Then, finally, the boundary disappears and operation can no longer be continued.

Examples 10-15 The experiment was conducted in the same manner as in Examples 2-9, except that the compositions of the uranium solutions and the reducing agent solution are changed to those as shown in Table 4 The results are shown in Table 5.

U(VI) concenExample tration No (M) 0 01 11 0 06 12 0 08 13 0 15 50) 14 0 30 0 30 Ti(III) concentration (M) 0.02 0.12 0.20 0.30 0.50 0.60 TABLE 4 hydrochloric acid concentration (M) Catal species 3.5 Fe CI 2 Alloxan 3.5 Fe CI 2 Alloxan 3.5 Fe CI 2 Alloxan 3.5 Fe CI 2 Alloxan 3.5 Fe CI 2 Alloxan 3.5 Fe CI 2 Alloxan k (I/mol min) 22.0 22.0 22.0 yst concentration (M) 0.3 0.1 0.3 0.1 0.3 0.1 0.3 0.1 0.3 0.1 0.3 0.1 22.0 22.0 22.0 4 TABLE 5

Example the boundary appearance of No K Ul VI isotopic ratio moving speed the boundary 40 0 007348 3 9 slightly unclear 5 11 24 0 007353 10 8 clear 12 18 0 007492 5 5 clear 13 10 0 007539 6 8 clear 14 7 2 0 007502 6 4 slightly unclear 10 6 7 0 007491 7 1 slightly unclear Examples 16-20 The anion-exchange resin used in Examples 2-9 was packed in the jacketed chromatographic column (inside diameter 20 mm) kept at 80 C, to the height of 92 15 cm, and thoroughly washed with 6 N hydrochloric acid.

By supplying the uranyl solution having the composition as shown in Table 6 thereby to substitute to uranyl ion form and then by supplying the reducing agent solution having the composition as shown in Table 6, the separation was conducted in the same manner as in Examples 2-9 All of the effluent of uranium was 20 collected by every 5 ml fraction and the concentrations of these fractions were determined by fluorescent X-ray analysis and colorimetric analysis Then, by measuring the isotope ratios subsequently from the nearest fraction to the boundary, the chromatograms of the total uranium concentration, uranyl concentration, the isotope ratios over the whole region of the enriched part, were 25 made, respectively.

The total amount of 235 U separated in the enriched part D is calculated by the following formula:

D=f(r-ro) Cud V r: the isotope ratio at V ml of the eluant volume 30 ro: the atom fraction of natural uranium ( 0 007200) Cu: total concentration of uranium in d Vm L of the eluant volume.

The effective separation factor E was calculated by the equation as previouslydescribed The reduction ratio R was determined by the ratio of uranous ion divided by uranyl ion, being constant from the chromatogram The results are 35 shown in Table 6.

TABLE 6 effective sepa 40 U(VI) Ti(III) reduc ration concenrt concen tion factor Example tration tration ratio (E) k ( 1/ No (M) (M) Catalyst (R) v-(v,,,x 10-4 mol min) 16 0 20 0 10 Fe CI 21 O M 1 6 4 1 6 6 25 0 45 17 0 20 0 15 Fe CI 2 L OM 2 1 3 7 7 4 25 0 18 0 20 0 20 Fe CI 2 L OM 2 4 3 6 7 7 25 0 19 0 20 0 31 Fe CI 2 L OM 3 6 3 4 8 9 25 0 0 20 0 40 Fe C 12 1 OM 6 5 2 9 7 5 25 0 Example 21 50

A conc titanium trichloride solution is prepared by dissolving spongy titanium in a concentrated hydrochloric acid A conc Ti(IV) solution is also prepared, by mixing 100, aqueous hydrogen peroxide solution with the conc titanium trichloride solution as prepared above in equivalent amounts until the violet colour of Ti(III) is faded to form a colourless, transparent solution 55 Mixtures (each 100 ml) of the thus prepared Ti(III) and Ti(IV) solutions with Ti(III) concentration of 0 2 M and Ti(IV) concentration of 0 2 M containing the titanium precipitation preventing agent, hydrochloric acid, and water in amounts as shown in Table 7 were prepared as samples In the test tubes equipped with a stopper, each having an inner volume of 200 ml, the said sample solutions were 1,565,391 introduced, respectively, and after dissolved oxygen and air were removed by highly purified nitrogen, the tubes were sealed tightly and dipped in a water bath kept at the temperature of 95 C The wall and the bottom of the said test tubes were observed with the naked eye to measure the time before the white precipitates of Ti(IV) appear The results are shown in Table 7 5 TABLE 7

Example

No.

1 (control) 2 (control) 3 4 6 7 8 9 11 titanium precipitation preventing agent concentration species (M) chromotropic acid catechol citric acid tiron tartaric acid sulfosalicylic acid sodium gluconate mannitol glucono-S-lactone glucono-y-lactone 0.2 0.5 0.2 0.1 0.2 0.2 0.15 0.15 0.15 0.15 concentration of hydrochloric acid (M) 4 1 3.5 4 4 4 4 4 4 4 the period of appearance of precipitates (hrs) 0.5 18 8 27 23 Example 22

In two chromatographic columns (column A and column B), each being equipped with a jacket and having an inner diameter of 200 mm and a length of 2000 mm, the same resin as used in Example 1 was filled up to the height of 1800 mm Into the said two columns kept at 100 C, were supplied the uranium solutions having the following compositions, respectively:

column A:

U(VI) O IOM; Fe(II) 0 20 M; HCI 4 O M column B:

U(VI) O IOM; Fe(II) 0 20 M; HC 1 4 O M; sodium gluconate 0 20 M, thereby to form an uranium adsorption zone, and further supplied the reducing agent solutions having the following compositions, respectively, such as:

column A:

Ti(III) 0 3 M; Fe(II) 0 2 M; HCI 4 O M column B:

Ti(III) 0 3 M; Fe(II) 0 2 M; HC 1 4 O M; sodium gluconate 0 20 M, thereby to form and then move the boundary The separation was conducted in each column by operating in the same manner as in Examples 2-9 and the isotopic ratio most closely adjacent to the boundary was measured In each operation, large amounts of Ti(IV) precipitates were formed on the inside wall of the column and the surface of the resin was coloured in a white-grey colour, so that it became difficult to observe the boundary with the naked eye After 4 N hydrochloric acid was supplied to the column A and the column B to remove remaining Ti(III), the above operation was further repeated twice The results of measurements of the isotopic ratios are shown in Table 8.

the number of operation times the first operation the second operation the third operation TABLE 8 isotopic ratio column A column B 0.007381 0 007429 0.007324 0 007418 0.007291 0 007433 It was found that the selectivity ratio KWM,1 was 12 8 and k had a value of 7 5 Vmol min.

1.565391 1 A

Claims (23)

WHAT WE CLAIM IS:-

1 A process for separating uranium isotopes in aqueous solution by forming a uranium adsorption zone having uranium complex anions adsorbed on an anionexchange material in contact with the front boundary between an oxidizing agent zone and said uranium adsorption zone, or the rear boundary between a reducing 5 agent zone and said uranium adsorption zone, or both boundaries, the said boundaries being moved by a continuous feed of a solution of uranium complex anions or a reducing agent solution as an eluant solution, thereby concentrating uranium-238 in the vicinity of the front boundary, uranium-235 in the vicinity of the rear boundary, or both thereof, wherein the electron exchange reactions occuring 10 in the uranium adsorption zone are accelerated to the rate constant k of not less than I mol/liter minute by use of one or more electron exchange catalysts, contained in the eluant solution, selected from (I) metal ions of iron, copper, indium, zirconium, germanium, vanadium, arsenic, molybdenum, rhenium, ruthenium, lanthanides, or the metal ions of an 15 atomic group of the periodic table containing said metals, provided that the ions of the atomic group with zero valency are excluded; ( 2) aliphatic, aromatic, or cyclic amines derivatives and salts thereof; ( 3) amino polycarboxylic acids, derivatives and salts thereof; ( 4) aliphatic or aromatic carboxylic acids, derivatives and salts thereof; 20 ( 5) aromatic oxysulfonic acids and salts thereof; ( 6) amino acids and salts thereof; ( 7) amino sulfonic acids and salts thereof; ( 8) P-diketones; ( 9) water-soluble, organic solvents; 25 ( 10) quinones; ( 11) polyhydroxy aromatics; and ( 12) ailoxans, under the conditions whereby the selectivity coefficient Kullv) is 2 or more.

2 A process as claimed in Claim 1, wherein an eluant solution of an uranium 30 isotope mixture containing U(IV) complex anions is fed to an anionexchange material on which an oxidizing agent has previously been retained to form a boundary between the uranium adsorption zone and the oxidizing agent zone, thereby to concentrate uranium-238 in the vicinity of said boundary.

3 A process as claimed in claim 1, wherein an eluant solution containing a 35 reducing agent is fed to the uranium adsorption zone having U(VI) complex anions adsorbed on the anion-exchange material to form a boundary between the uranium adsorption zone and the reducing agent zone, thereby to concentrate uranium-235 in the vicinity of said boundary.

4 A process as claimed in Claim 1, wherein a solution of a uranium isotope 40 mixture containing U(IV) complex anions is fed to an anion exchange material on which an oxidizing agent has previously been retained to form one boundary between the uranium adsorption zone and the oxidizing agent zone, and an eluant solution containing a reducing agent is further fed to the uranium adsorption zone to form the other boundary between the uranium adsorption zone and the reducing 45 agent zone thereby to concentrate uranium-238 in the vicinity of the front boundary and uranium-235 in the vicinity of the rear boundary.

A process as claimed in any of Claims 1 to 4, wherein the oxidizing agent is at least one agent consisting of a salt of divalent copper, trivalent iron, tetravalent cerium, divalent manganese, tetravalent vanadium, hexavalent molybdenum or 50 trivalent thallium.

6 A process as claimed in any one of Claims 1 to 5, wherein the oxidizing agent is a trivalent iron salt.

7 A process as claimed in any of Claims 1 to 6, wherein the reducing agent is at least one agent consisting of a trivalent vanadium salt, pentavalent 55 molybdenum salt, trivalent titanium salt or divalent tin salt.

8 A process as claimed in any of Claims 1 to 7, wherein the reducing agent is a trivalent titanium salt.

9 A process as claimed in any of Claims 1 to 8, wherein the concentrations of the oxidizing agent, uranium ion and the reducing agent are from 0 02 to 2 0 60 mol/liter, from 0 01 to

1 0 mol/liter and from 0 02 to 1 0 mol/liter, respectively.

A process as claimed in Claim 9, wherein the concentration of uranium ion is in the range from 0 10 to 0 50 mol/liter.

11 A process as claimed in any of Claims 1 to 10, wherein the separation is operated in the presence of 1 to 6 mol/liter hydrochloric acid or hydrobromic acid 65 1,565,391 in the external solution as hereinbefore defined in contact with the anion-exchange material.

12 A process as claimed in any of Claims 1 to 11, wherein the separation is operated at a temperature at 60 C or above.

13 A process as claimed in Claim 8, wherein the separation is operated at a 5 temperature of 60 C or above in the presence of an agent at a concentration of 0 1 to 3 mol/litre which prevents titanium precipitation.

14 A process as claimed in Claim 13, wherein the agent is at least one compound consisting of oxalic acid, tartaric acid, citric acid, malonic acid, glutaric acid, succinic acid, maleic acid, fumaric acid, salicylic acid 5sulfosalicylic acid, 10 or a salt of one of these acids, catechol, resorcinol, 4,5-dihydroxy-mbenzenedisulfonic acid disodium salt chromotropic acid, glucose, fructose, mannose, galactose, arabinose, ribose, xylose, erythrose, sorbitol, mannitol, arabitol, glucono-S-lactone, glucono-y-lactone, gluconic acid, mannonic acid, uronic acid, a-keto gluconic acid or methyl glucoside

15 A process as claimed in any of Claims 1 to 14, wherein the ratio of uranous ion concentration to uranyl ion concentration is substantially equal to the square root of the selectivity coefficient.

16 A process as claimed in any of Claims 1 to 15, wherein the electron exchange catalyst is at least one catalyst consisting of metal ions of molybdenum, 20 vanadium, copper, indium, rhenium, yittrium, ruthenium, arsenic, or of the ions of a metal of an atomic group of the periodic table containing said metals, provided that the atomic groups with zero valency are excluded.

17 A process as claimed in any of Claims I to 15, wherein the electron exchange catalyst is at least one catalyst consisting of piperidine, piperazine, 25 ethylene diamine, propylene diamine, 1,3-diaminopropane, ethanolamine, pphenylenediamine, imidazole, pyridine, a, /3, y-picoline; a derivative thereof; a salt thereof; acetic acid, gluconic acid, tartaric acid, citric acid, 5sulfosalicylic acid; a derivative thereof; a salt thereof; 4,5-dihydroxy-m-benzene-disulfonic acid disodium salt chromotropic acid; a salt thereof; ethylene glycol, methanol, ethanol, 30 propanol, acetone or acetonitrile; p-benzoquinone, duroquinone, chloranyl, chloranylic acid or /3-napthoquinone; hydroquinone, catechol or resorcinol; alloxan, methyl alloxan, alloxantin or methyl alloxantin.

18 A process as claimed in any of Claims 1 to 16, wherein the electron exchange catalyst contains ions of iron 35

19 A process as claimed in any of Claims 1 to 15, wherein the electron exchange catalyst is a combination of at least one catalyst from the group as defined in Claim 16 with at least one catalyst from the group as defined in Claim 17.

A process as claimed in Claim 18, wherein the electron exchange catalyst is a combination of ions of iron with at least one catalyst from the group as defined in 40 Claim 16.

21 A process as claimed in Claim 18, wherein the electron exchange catalyst is a combination of ions of iron with at least one catalyst from the group as defined in Claim 17.

22 A process for separating uranium isotopes, as claimed in Claim 1, 45 substantially as herein described with reference to any of Examples 1 to 20 and 22.

23 Uranium isotopes separated by a process as claimed in any of Claims I to 22.

ELKINGTON AND FIFE, Chartered Patent Agents, High Holborn House, 52/54 High Holborn, London, WCIV 65 H.

Agents for the Applicants.

Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1980 Published by The Patent Office, 25 Southampton Buildings, London WC 2 A l AY, from which copies may be obtained.

1,565,391